Lionheart
Solid Ocelot
I would say he is just a regular halfbreed who lived a average lifespan. That does not rule out he could be possessed by Vergil because Vergil would be more willing to posses a half-breed because their bodies are stronger than human beings.
The problem with the game was that they didn't commit to the character and the story so it suffers from lazy writing. The question of Nero being vergil/dante's kid could have been solved by just stating their ages in the game itself. You have data files on the characters so you could have just done that.
The game relies too much on trish's appearance to set up the timeline when it could have just done that through dialogue or taunts. Without her there is nothing that tells you when it takes place.
Yeah. In the end, DMC4 just doesn't make sense. Nor does DMC3 if you consider that Dante hadn't seen Vergil in DMC1 since they were eight. I do want to make it clear, though, that it was stated DMC4 takes place ten years after DMC3, and Dante is 19 in DMC3, so that would make him around 29 in DMC4. In DMC1, Trish says Dante lost a brother and mother to evil twenty years ago. As Dante was eight, he must be about 28 in DMC1. Dante and Vergil age normally.